dissenting.
I respectfully dissent. In my view, the Merit Systems Protection Board was correct to conclude that,, in light of the historical background of the military leave statute, the four petitioners were not denied military leave to which they were entitled.
This case turns on the meaning of the allowance of 15 days per year for military leave in the version of 5 U.S.C. § 6323 that was in effect before the statute was amended in 2000. The court states that the question in this case is “whether an employee must be answerable to the government at all for time that he or she is not required to work,” and then answers that question by stating: “As a general matter, employees are not accountable to their employers for time they are not required to work. We see no reason why federal employees need military leave for days on which they are not scheduled to work.” But that is not a fair charaeteriza*1344tion of the question presented in this case. The version of the military leave statute that was applied to the petitioners in this case did not require them to be “accountable” to the government for days on which they were not required to work. The statute simply provided a set period of time during which Congress wanted to ensure employees would receive paid leave from their civilian jobs for purposes of engaging in military training. The question in this case is how to calculate that period. Based on an imposing amount of evidence, the Merit Systems Protection Board concluded that Congress intended the period to be calculated by counting from the beginning of the military leave period to the end, without skipping intervening non-workdays. Reaching the proper result in this case requires us to decide what Congress intended with respect to a question of counting mechanics; it does not require us to conclude that Congress viewed federal employees on military leave as “accountable” to the government for days that they did not work. Moreover, the fact that the court finds the Board’s interpretation of the statute to be contrary to general leave practices in employment, including federal civilian employment, ignores the fact that, at the time the military leave statute was enacted, the “general” practice to which the court alludes was the exception, not the rule.
A
Before 1899, federal civilian employees were charged annual and sick leave for all calendar days, including non-workdays, that occurred during the leave period. See Act of Mar. 3, 1883, ch. 126, § 4, 22 Stat. 531, 564 (authorizing a “leave of absence ... which shall not exceed thirty days in any one year”); Act of Mar. 3, 1893, ch. 211, § 5, 27 Stat. 675, 715 (authorizing heads of departments to grant 30 days’ annual leave and 30 days’ sick leave annually to employees); Act of Mar. 15, 1898, ch. 68, § 7, 30 Stat. 277, 316-17 (authorizing “thirty days’ annual leave with pay in any one year,” which period may be extended because of illness by an additional period “not exceeding thirty days in any one case or in any one calendar year”); Act of July 7, 1898, ch. 571, 30 Stat. 652, 653 (clarifying that a period of 30 days’ annual leave may be granted to an employee who has had no more than 30 days’ leave with pay on account of sickness during the same year); 20 Op. Att’y Gen. 716, 718 (1894) (ruling that the correct interpretation of the law is “to charge Sundays and holidays against the absentee when they intervene during the period of absence”); 22 Op. Att’y Gen. 77, 79 (1898); Leaves of Absence Include Sundays & Legal Holidays, 5 Comp. Treas. 436, 436-37 (1899). The opinion of the Comptroller of the Treasury, which contains the most detailed analysis among the contemporaneous constructions of the early statutes, was based in large part on the general legal principle that “[wjhere the time limited by statute for a particular purpose is such as must necessarily include one or more Sundays, they are to be included in the enumeration, unless they are expressly excluded or the intention of the legislature to exclude them is manifest.” 5 Comp. Treas. at 442; see also Computation of Leaves of Absence to Employees of MailBag & Mail-Lock Repair Shops, 13 Comp. Treas. 799, 800 (1907).
In 1899, Congress explicitly changed that rule with respect to annual leave for federal civil servants. See Act of Feb. 24, 1899, ch. 188, 30 Stat. 846, 890. As the Board notes, however, the 1899 statute did not apply to sick leave, and the agencies therefore continued to charge employees with sick leave for non-workdays intervening during a period of leave. That practice was not changed until 1951. Moreover, statutes that did not specify that leave periods included only “workdays” contin*1345ued to be construed to include non-workdays in computing leave periods. See To the Attorney Gen., Comp. Gen. B-133,674 (1957); 13 Comp. Treas. at 800; 5 Comp. Treas. at 436-37; 20 Op. Att’y Gen. at 718.
The first statute granting military leave for civilian employees of the federal government was enacted in 1917. Act of May 12, 1917, ch. 12, 40 Stat. 72. That statute granted up to 15 days of military leave each year for members of the Officers’ Reserve Corps “on all days during which they shall be ordered to duty with troops or at field exercises, or for instruction.” Although the statute did not state whether intervening non-workdays during a period of military leave were to be charged as leave, the statute was consistently applied in accordance with the pre-1899 system for calculating annual leave and the then-existing policy for calculating sick leave. See To the Attorney Gen., Comp. Gen. No. B-133, 674; To the Sec’y of the Army, 27 Comp. Gen. 245, 252-53 (1947). Calculating military leave in that way, moreover, was consistent with the training requirements for federal employees who were members of reserve and national guard units. Those training requirements, which had just been adopted in the previous year, featured one extended 15-day training period per year for which the employee would have to take leave from his civilian job. See Act of June 3,1916, ch. 134, § 31, 39 Stat. 166, 187 (members of the regular Army Reserve subject to field training for up to 15 days per year); id. § 39, 39 Stat. at 191 (members of Officers’ Reserve Corps subject to duty or instructional service of up to 15 days per year); id. § 55, 39 Stat. at 195-96 (members of Enlisted Reserve Corps subject to be ordered to instructional or training periods of up to 15 days per year); id. § 92, 39 Stat. at 206 (members of National Guard subject to 48 drills plus an instructional period of at least 15 days in training each year).
The same pattern — of requiring training periods of 15 days per year and granting a corresponding period of 15 days of military leave — continued unchanged in any essential respect for many years. See Act of Feb. 28, 1925, § 20, 43 Stat. 1080, 1085 (members of the Fleet Naval Reserve required to perform training not to exceed 15 days annually); id. § 36, 43 Stat. 1089-90 (members of Fleet Naval Reserve entitled to leave of absence from their federal employment for periods not to exceed 15 days in any one calendar year); Naval Reserve Act of 1938, § 9, 52 Stat. 1175, 1177; Armed Forces Reserve Act of 1952, Pub.L. No. 82-476, § 233(c), 66 Stat. 481, 490. The Comptroller General, although requested to reconsider that office’s interpretation of the military leave statute on several occasions, continued to construe the statute as requiring that non-workdays within a period of military leave be counted against the 15-day military leave allotment. See To the Sec’y of the Army, 29 Comp. Gen. 269, 271 (1949) (finding it “significant” that a recent amendment to the military leave statute “contains no express or implied language that the theretofore method of charging military leave upon a calendar basis, which was well known to the Congress, was in anywise to be changed”); To the Sec’y of the Army, 27 Comp. Gen. at 252-53; To the Sec’y of Agriculture, 16 Comp. Gen. 1039, 1041 (1937); To the Postmaster Gen., 9 Comp. Gen. 448, 448 (1930).
In 1956, the various training statutes were consolidated into a single section as part of the recodification of Titles 10 and 32 of the United States Code. See Act of Aug. 10, 1956, Pub.L. No 84-1028, 70A Stat. 1 (1956). The 15-day training requirements were codified at 10 U.S.C. § 672(b) (1958) and 32 U.S.C. § 502(a)(2) (1958). The 15-day period of allowable military leave was found at Pub.L. No. 84-1028, § 29(a), 70A Stat. 632 (1956), and *1346was codified at 5 U.S.C. § 32r(a) (1958). The latter statute, which is now 5 U.S.C. § 6323(a), read in 1956 as follows:
Each Reserve of the armed forces or member of the national guard who is an officer or employee of the United States or the District of Columbia, permanent or temporary indefinite, without regard to classification or terminology peculiar to the Civil Service system, is entitled to leave of absence from his duties, without loss of pay, time, or efficiency rating for each day, but not more than 15 days in any calendar year, in which he is on active duty or is engaged in field or coast defense training under sections 502-505 of title 32, United States Code.
The period of military leave authorized in that statute, as in its predecessors, was construed as being 15 calendar days, not 15 workdays. In a 1957 opinion dealing with the Fleet Reserve, the Comptroller General explained:
Not only is it apparent from the plain language of the statute that the fifteen-day period of leave relates to, and must be governed by, the fifteen-day period of training duty, but the legislative history also supports this view.... We think it is evident ... that the intention of Congress was to grant, authority for the performance by Naval reservists of training duty for periods of not to exceed 15 days and, to provide, so far as government employees are concerned, that their pay, time, or efficiency rating should not be adversely affected by reason of their performing such duty. Thus, both the plain language and legislative history of the statute, viewed in the light of the preceding statutes with which it is entirely consistent and on which it was undoubtedly patterned, make it clear that the phrase “from his duties” may not be construed as an express exclusion of Sundays and holidays from the computation of leave for periods of military training ordered thereunder.
To the Attorney Gen., Comp. Gen. No. B-133,674.
In 1951, as part of an overhaul of the federal leave system, Congress provided that both annual and sick leave for federal employees would be charged without counting non-workdays. See Pub.L. No. 82-233, §§ 203-209, 65 Stat. 672, 679-83 (1951). The new statute specifically provided that the “days of leave provided for [in the statute] shall mean days upon which an employee would otherwise work and receive pay, and shall be exclusive of holidays and all nonworkdays established by Federal statute or by Executive or administrative order.” Id. § 205(a), 65 Stat. at 681. The 1951 statute applied only to annual and sick leave and did not apply to other forms of leave, such as military leave.
From this background, it is evident that, as of 1957, the rules applicable to military leave were clear: The 15-day period of military leave was routinely charged on the basis of calendar days, so that intervening non-workdays were counted against the 15-day period. Non-workdays at the beginning or end of the period, however, were not counted. Therefore, if an employee whose normal work week was Monday through Friday began his or her military training service on a Monday and returned to work two Mondays later, the employee would be charged for the intervening weekend days, but not the weekend days at the beginning or end of the military leave period.
That was the state of the law as of 1957, and I do not understand the court to disagree. If that is correct, then the Board’s decision in this case must be upheld unless we can say that, at some point between 1957 and 1999 (the leave year at issue in this case), a change was made that re*1347quired the military leave statute to be construed differently. As detailed below, no such change occurred.
B
In 1966, the military leave statute was recodified as 5 U.S.C. § 6323(a). Pub.L. No. 89-554, 80 Stat. 378, 522 (1966). In 1968, Congress made two relevant changes in the leave statutes. First, it amended section 6323 to grant military leave of up to 22 workdays to reservists or members of the National Guard who are activated for law enforcement purposes. Second, it enacted section 6326, which granted up to three days paid leave for employees to attend the funeral of an immediate relative in the Armed Forces who died as a result of injuries incurred in a combat area. Pub.L. No. 90-588, 82 Stat. 1151 (1968).
Significantly, the 1968 legislation distinguished between the 22 “workdays” of leave that reservists would be granted, which the House Committee report and proponents of the legislation pointed out would amount to approximately 30 calendar days, and the 15 “days” of military leave ordinarily provided for training, which the Chairman of the Civil Service Commission pointed out meant 15 calendar days. See H.R.Rep. No. 90-1560, at 6, 10, 12 (1968). The House Committee report thus reflects a clear understanding that the 15 days of military leave provided by section 6323(a) was, and would continue to be, calculated on the basis of calendar days, not workdays.
In the course of Congress’s consideration of the 1968 legislation, a question arose as to whether the amount of military leave provided under section 6323(a) was adequate. To address that issue, the Senate Committee on Post Office and Civil Service directed the Civil Service Commission to report back to the Committee as to whether there was a need to provide more paid leave to federal employees for military training. See S.Rep. No. 90-1443, at 2 (1968), reprinted in 1968 U.S.C.C.A.N. 4288, 4289. In its response, the Commission submitted a detailed report, in which the Commission made clear that military leave was charged on a calendar day basis and concluded that there was no need to change that practice. See Civil Service Comm’n, Bureau of Policies & Standards, Military Leave for Reservists & National Guardsmen — June 1969, reprinted in Improve Administration of Leave System for Federal Employees: Hearings Before the Subcomm. on Employee Benefits of the House Comm, on Post Office & Civil Service, 92d Cong. 25-36 (1972). The report stated:
The suggestion that military leave be charged on a workday rather than a calendar day basis is, in effect, a request for additional military leave. It has been shown, in previous sections of this report, that 15 days of military leave is sufficient to meet the “normal” requirements of the Reserves or National Guard. Any increase in the amount of military leave with pay would result in increased cost to the Government....
The 15 calendar days of military leave allowable adequately met the needs of the vast majority of reservists and National Guardsmen in 1968.
Id. at 29. No statutory change was made as a result of the Commission’s report.
The court does not suggest that the 1968 amendment altered the prior regime. In fact, it acknowledges that the Board’s interpretation “may have been correct for the original version of section 6323(a) enacted in 1968.” However, the court concludes that an important change in the statute was made in 1980, when the language of the military leave statute was altered.
The pre-1980 version of section 6323(a) provided that a federal civilian employee *1348“is entitled to leave without loss of pay, time, or performance or efficiency rating for each day, not in excess of 15 days in a calendar year, in which he is one active duty or is engaged in field or coast defense training” with the Reserves or the National Guard. The 1980 amendment changed that formulation. It omitted the language “for each day, not in excess of 15 days a calendar year, in which he is on active duty or is engaged in field or coast defense training.” In place of that language, the 1980 amendment inserted the words “for active duty or engaging in field or coast training,” and added a new sentence stating, “Leave under this subsection accrues for an employee or individual at the rate of 15 days per fiscal year and, to the extent that it is not used in a fiscal year, accumulates for use in the succeeding fiscal years until it totals 15 days at the beginning of a fiscal year.” Pub.L. No. 96-431, 94 Stat. 1850,1850 (1980).
The court finds that through that amendment Congress “changed the computation of leave days from a variable measurement pegged to the actual length of military training, to a constant measurement of 15 days,” and thereby changed the method of calculating military leave from counting calendar days to counting workdays. According to the court, “While leave computed by the actual period of reserve training necessarily includes non-workdays in the calculation, leave measured by an absolute number of days (15) does not.”
I disagree that the 1980 amendment made that fundamental change in the meaning of the statute. Nothing about the language used in the 1980 formulation, under which “leave accrues ... at the rate of 15 days per fiscal year” requires that the 15 days be interpreted to as workdays rather than calendar days. The most that can be said for the new language is that it is possible to read the 1980 formulation as excluding non-workdays, while it is more difficult to read the pre-1980 language in that fashion. But that proposition falls far short of establishing that the 1980 statute must be given the interpretation that the court assigns to it.
The legislative history of the 1980 Act is highly instructive on this point. The House Report on the legislation explicitly states that the legislation was intended to make only “three changes in existing law.” H.R.Rep. No. 96-1128, at 2 (1980), reprinted in 1980 U.S.C.C.A.N. 3871, 3871. It was intended (1) to make military leave available on a fiscal year basis rather than a calendar year basis; (2) to allow federal employees to carry over some or all of their military leave to the succeeding fiscal year; and (3) to grant part-time employees a proportional share of the military leave provided to full-time employees. Id. The principal problem addressed was the hardship that occurred when employees had to attend two training sessions in the same calendar year and could not carry over military leave to accommodate the scheduled sessions. There is no indication in the brief report of any intention to change the method of computing the 15 days of allowable military leave from calendar days to workdays.
The hearing that was held on the bill that became the 1980 amendment to section 6323 makes clear that the focus of the legislation was on allowing military leave to be carried over, and that no change was intended to the method of calculating military leave. See Retirement Appeals, Military Leave, & Quadrennial Pay Comm’n, Hearing Before the Subcomm. on Compensation & Employee Benefits of the Comm, on Post Office & Civil Service, House of Representatives, 96th Cong. 4-10 (1980). Moreover, the witnesses who appeared before the subcommittee made clear that they regarded as settled — and not at issue in the proposed legislation— *1349that the 15 days of military leave were to be used for the 15-day training period required for members of the Reserves and the National Guard. See id. at 9, 11, 12. As in the House report, there was no suggestion at the hearing that any change in the method of calculation was intended. It thus seems clear that the change in the language of section 6323(a) was made solely to provide additional flexibility for employees whose units might schedule two 15-day training sessions in a single calendar year and who might have to carry over military leave from one year to another. The contrary construction is by no means required by the language of the 1980 Act, and in light of the complete absence of any indication of an intention to change the longstanding method of calculating military leave, the 1980 Act cannot fairly be interpreted as effecting that change.
In the aftermath of the 1980 amendment to section 6323, the Comptroller General on several occasions revisited the issue of how to calculate military leave, and consistently ruled that the “calendar day” system that was in place before 1980 was still in effect after the 1980 revision. See In re Military Leave—Active Duty Spans Two or More Fiscal Years, 71 Comp. Gen. 513, 515 (1992); In re Haas, Comp. Gen. B-212,851 (1984); In re McMillian, Comp. Gen. B-211,249 (1983); In re AFGE Local 1364, 61 Comp. Gen. 558, 559 (1982); In re Campbell, 60 Comp. Gen. 381, 384 (1981).
Section 6323(a) was amended in minor respects after 1980, but none of those amendments has any arguable effect on this case. Accordingly, if as I believe is clear, the 1980 statute did not alter the method of calculating military leave, we must adhere to the pre-1980 system of calculation, which the court recognizes “necessarily includes non-workdays in the calculation.”
C
The court focuses on another piece of evidence that it regards as instructive with regard to the question before us: the administrative construction of 5 U.S.C. § 6326, a statute that provides federal employees up to three days of leave to attend funerals or memorial services for close relatives who are members of Armed Forces and who die from injuries incurred in a combat zone. Section 6326 does not specify whether the three days are to be counted as workdays or calendar days, but the Civil Service Commission and the Office of Personnel Management have consistently interpreted the term “day” in the statute to mean “workday.” 5 C.F.R. § 630.804. The court notes the apparent inconsistency in the agency’s position with respect to the calculation of military leave and funeral leave.
It is true that OPM’s funeral leave regulation defines the word “day” in section 6326 to mean “workday,” not “calendar day,” and that neither OPM in its regulations nor the government on appeal has provided any explanation for why OPM construed the term “day” differently for purposes of sections 6323 and 6326. While the reason for this apparent inconsistency is unexplained,1 nothing in the principles underlying the Chevron doctrine authorizes a court to use an agency’s regulatory construction of one statute (here, section 6326) to trump its consistent, longstanding *1350construction of a different statute (here, section 6323). Even if the agency’s construction of section 6326 is at odds with the rationale underlying its construction of section 6323, there is no justification for giving the agency’s construction of section 6326 greater respect in construing section 6323 than the agency’s construction of section 6323 itself.
The court also regards as an inconsistency the fact that the government’s position with respect to the calculation of military leave is that employees are charged for non-workdays occurring within the period of military leave, but not for non-workdays occurring at the beginning or end of the period of military leave. Thus, if an employee who works a normal Monday through Friday schedule begins a 15-day military training period on a Sunday and concludes that training period two Sundays later, the employee is charged for the intervening weekend, but not for the Sunday at the outset of the training period nor for the Sunday at the end of that period.
In fact, there is no inconsistency in the traditional practice of not charging military leave for non-workdays at the outset and the end of a period of military training. As noted earlier, that practice has been used since the outset of the military leave system, and merely reflects the view that (1) the period of the employee’s absence from work does not begin until a day that the employee is required to be at work, and (2) an employee is not regarded as having been absent during a non-workday if the employee returns to work on the first workday following a non-workday. See In re McMillian, Comp. Gen. B-211, 249; In re AFGE Local 1364, 61 Comp. Gen. at 559; In re Campbell, 60 Comp. Gen. at 384; To the Attorney Gen., Comp. Gen. B-133,674; To the Sec’y of the Army, 27 Comp. Gen. at 252-53. While that approach reflects a relatively generous construction of the military leave statute, it is not an unreasonable application of the traditional “calendar day” standard.
D
The court disposes of the longstanding administrative interpretation of the military leave statute by noting that OPM lacks formal rulemaking authority with respect to that statute and that the administrative interpretation of the statute is therefore not entitled to the level of respect that would be due to an interpretation embodied in formal regulations. While OPM’s position would be virtually impregnable if it had issued a formal regulation pursuant to statutory authority adopting the traditional method of calculating military leave, the absence of a formal regulation does not mean that the longstanding administrative construction of the military leave statute has no more force than the “interpretations contained in policy statements, agency manuals, and enforcement guidelines” that have been held to be “beyond the Chevron pale.” United States v. Mead Corp., 533 U.S. 218, 234, 121 S.Ct. 2164, 150 L.Ed.2d 292 (2001). As noted, the Comptroller General, in a series of detailed opinions issued over many years, has consistently interpreted the military leave statute in the manner urged by the government in this case. In addition, the Civil Service Commission took the same position when asked by Congress for its views and, until the recent statutory amendment to section 6323 in 2001, OPM had consistently interpreted the military leave statute throughout the lifetime of the statute as requiring computations that included non-workdays occurring within the leave period. The administrative interpretation of the statute therefore constitutes much more than the kind of informal statement of agency policy that was at issue in James v. Von Zemenszky, 301 F.3d 1364 (Fed.Cir.2002), *1351and is entitled to be given considerable weight. See Barnhart v. Walton, 535 U.S. 212, 221, 122 S.Ct. 1265, 152 L.Ed.2d 330 (2002); see also Mead, 533 U.S. at 234-35, 121 S.Ct. 2164; Reno v. Koray, 515 U.S. 50, 61, 115 S.Ct. 2021, 132 L.Ed.2d 46 (1995). Moreover, it is significant that throughout the 84-year period between 1917 and 2001, Congress took no action to alter the “calendar day” basis for calculating military leave, even though that method was consistently used throughout the government, even though the use of that method was called to Congress’s attention on several occasions, and even though Congress frequently amended the military leave statute to correct other perceived flaws in the Act. See Lorillard v. Pons, 434 U.S. 575, 580-81, 98 S.Ct. 866, 55 L.Ed.2d 40 (1978).
In sum, when Congress enacted the military leave statute it was clear that leave was to be calculated by counting intervening non-workdays within the leave period. During the ensuing 84 years, Congress did not change that rule, and the various administrative agencies that had occasion to address the statute consistently interpreted it in that fashion. While that method of leave computation may seem anachronistic to us in light of changes in the method of calculating other leave periods, it was the method Congress chose for military leave, and it was the method that was in effect at the time of the events in this case.
I would affirm the Board’s decision.
. It may be that the reason for the difference lies in the shortness of the three-day period in the funeral leave statute. In early administrative constructions of the federal leave statutes, the Attorney General noted that statutory time periods are usually computed by including Sundays and holidays unless the periods are very short. 22 Op. Att’y Gen. at 79, 20 Op. Att'y Gen. at 718. The same principle applies to computations of time under the Federal Rules of Civil and Criminal Procedure. See Fed.R.Civ.P. 6(a); Fed.R.Crim.P. 45(a).